Methods for growing a nitrogen doped single crystal silicon ingot using continuous Czochralski method

Abstract

A method for growing a single crystal silicon ingot by the continuous Czochralski method is disclosed. The melt depth and thermal conditions are constant during growth because the silicon melt is continuously replenished as it is consumed, and the crucible location is fixed. The critical v/G is determined by the hot zone configuration, and the continuous replenishment of silicon to the melt during growth enables growth of the ingot at a constant pull rate consistent with the critical v/G during growth of a substantial portion of the main body of the ingot. The continuous replenishment of silicon is accompanied by periodic or continuous nitrogen addition to the melt to result in a nitrogen doped ingot.

We claim: 
     
       1. A method of preparing a single crystal silicon ingot by the Continuous Czochralski method, the method comprising:
 adding an initial charge of polycrystalline silicon to a crucible, the initial charge further comprising a source of nitrogen; 
 heating the crucible comprising the initial charge of polycrystalline silicon and the source of nitrogen to cause a silicon melt to form in the crucible, the silicon melt comprising an initial volume of molten silicon and having an initial melt elevation level; 
 contacting a silicon seed crystal with a silicon melt; 
 withdrawing the silicon seed crystal to grow a neck portion, wherein the silicon seed crystal is withdrawn at a neck portion pull rate during growth of the neck portion, and further wherein the neck portion has a neck portion nitrogen concentration of at least about 1×10 13  atoms/cm 3 , wherein the neck portion nitrogen concentration varies by no more than 20% above and no less than 20% below an average neck portion nitrogen concentration; 
 withdrawing the silicon seed crystal to grow an outwardly flaring seed-cone adjacent the neck portion, wherein the silicon seed crystal is withdrawn at a seed-cone pull rate during growth of the outwardly flaring seed-cone, and further wherein the outwardly flaring seed-cone has an outwardly flaring seed-cone nitrogen concentration of at least about 1×10 13  atoms/cm 3 , wherein the outwardly flaring seed-cone nitrogen concentration varies by no more than 20% above and no less than 20% below an average outwardly flaring seed-cone nitrogen concentration; and 
 withdrawing the silicon seed crystal to grow a main body of the single crystal silicon ingot adjacent the outwardly flaring seed-cone, wherein the silicon melt comprises a volume of molten silicon and a melt elevation level during growth of the main body of the single crystal silicon ingot, and further wherein the main body of the single crystal silicon has a main body nitrogen concentration of at least about 1×10 13  atoms/cm 3 , wherein the main body of the single crystal silicon ingot is at least about 1000 millimeters long, and further wherein the main body nitrogen concentration varies by no more than 20% above and no less than 20% below an average main body nitrogen concentration over at least 40% of axial length of the main body of the single crystal silicon ingot; 
 wherein the main body of the single crystal silicon ingot is grown at an initial variable main body pull rate and a constant main body pull rate, wherein the main body of the single crystal silicon ingot is grown at the initial variable main body pull rate for less than about 20% of a length of the main body of the single crystal silicon ingot and grown at the constant main body pull rate during growth for at least about 30% of the length of the main body of the single crystal silicon ingot, wherein the constant main body pull rate is between about 0.4 mm/min and about 0.8 mm/min, and further wherein the main body of the single crystal silicon ingot has a diameter of at least about 150 millimeters; and 
 further wherein polycrystalline is continuously fed or periodically feed to the crucible to thereby replenish a volume of molten silicon and to thereby maintain a melt elevation level in the crucible during growth of the main body of the single crystal silicon ingot and the source of nitrogen is continuously fed or periodically fed to the crucible to thereby replenish an amount of nitrogen. 
 
     
     
       2. The method of  claim 1  wherein the source of nitrogen is a solid source of nitrogen. 
     
     
       3. The method of  claim 1  wherein the source of nitrogen is silicon nitride powder. 
     
     
       4. The method of  claim 1  wherein the source of nitrogen is a silicon wafer having a silicon nitride film on a surface thereof, wherein the silicon wafer is optionally crushed. 
     
     
       5. The method of  claim 1  wherein the source of nitrogen is silicon oxynitride glass. 
     
     
       6. The method of  claim 1  wherein the source of nitrogen is nitrogen gas. 
     
     
       7. The method of  claim 1  wherein the neck portion nitrogen concentration is between about 1×10 13  atoms/cm 3  and about 1×10 15  atoms/cm 3 . 
     
     
       8. The method of  claim 1  wherein the outwardly flaring seed-cone nitrogen concentration is between about 1×10 13  atoms/cm 3  and about 1×10 15  atoms/cm 3 . 
     
     
       9. The method of  claim 1  wherein the source of nitrogen is continuously fed or periodically fed to the crucible in an amount between about 1 milligram nitrogen and about 100 milligrams nitrogen per 50 mm of axial length of the main body of the single crystal silicon ingot. 
     
     
       10. The method of  claim 1  wherein silicon nitride is continuously fed or periodically fed to the crucible during growth of the main body of the single crystal silicon ingot in an amount between about 2.5 milligrams silicon nitride and 250 milligrams silicon nitride per 50 mm of axial length of the main body of the single crystal silicon ingot. 
     
     
       11. The method of  claim 1  wherein the main body nitrogen concentration is between about 1×10 13  atoms/cm 3  and about 1×10 15  atoms/cm 3 . 
     
     
       12. The method of  claim 1  wherein the main body nitrogen concentration is between about 5×10 13  atoms/cm 3  and about 1×10 14  atoms/cm 3 , over at least 40% of axial length of the main body of the single crystal silicon ingot. 
     
     
       13. The method of  claim 1  wherein the main body nitrogen concentration is between about 1×10 13  atoms/cm 3  and about 1.5×10 14  atoms/cm 3 , and further wherein the main body nitrogen concentration varies by no more than 20% above and no less than 20% below an average main body nitrogen concentration over at least 40% of axial length of the main body of the single crystal silicon ingot. 
     
     
       14. The method of  claim 1  wherein the main body nitrogen concentration is between about 5×10 13  atoms/cm 3  and about 1×10 14  atoms/cm 3  and further wherein the main body nitrogen concentration varies by no more than 20% above and no less than 20% below an average main body nitrogen concentration over at least 40% of axial length of the main body of the single crystal silicon ingot. 
     
     
       15. The method of  claim 1  wherein a magnetic field is applied to the silicon melt during growth of the main body of the single crystal silicon ingot, and further wherein the main body of the single crystal silicon ingot comprises a main body interstitial oxygen concentration between about 10 PPMA and about 35 PPMA, and further wherein the main body interstitial oxygen concentration varies by no more than 20% above and no less than 20% below an average main body oxygen concentration. 
     
     
       16. The method of  claim 15  wherein a horizontal magnetic field is applied to the silicon melt during growth of the main body of the single crystal silicon ingot. 
     
     
       17. The method of  claim 15  wherein a cusp magnetic field is applied to the silicon melt during growth of the main body of the single crystal silicon ingot. 
     
     
       18. The method of  claim 15  wherein the applied magnetic field maintains a substantially constant melt/solid interface profile during at least about 70% of the growth of the main body of the single crystal silicon ingot. 
     
     
       19. The method of  claim 15  wherein the applied magnetic field maintains a substantially constant melt/solid interface profile during between about 70% and about 90% of the growth of the main body of the single crystal silicon ingot. 
     
     
       20. The method of  claim 1  wherein the main body of the single crystal silicon ingot is at least 1400 millimeters long. 
     
     
       21. The method of  claim 1  wherein the main body of the single crystal silicon ingot has a diameter of at least about 200 millimeters. 
     
     
       22. The method of  claim 1  wherein the constant main body pull rate is between about 0.4 mm/min and about 0.7 mm/min. 
     
     
       23. The method of  claim 1  wherein the main body of the single crystal silicon ingot is grown at the initial variable main body pull rate for between about 5% and about 20% of the length of the main body of the single crystal silicon ingot. 
     
     
       24. The method of  claim 1  wherein the main body of the single crystal silicon ingot is grown at the constant main body pull rate during growth for at least about 50% of the length of the main body of the single crystal silicon ingot. 
     
     
       25. The method of  claim 1  wherein the main body of the single crystal silicon ingot is grown at the constant main body pull rate during growth for at least about 70% of the length of the main body of the single crystal silicon ingot. 
     
     
       26. The method of  claim 1  wherein the main body of the single crystal silicon ingot is grown at the constant main body pull rate during growth for at least about 80% of the length of the main body of the single crystal silicon ingot. 
     
     
       27. The method of  claim 1  wherein the main body of the single crystal silicon ingot is grown at the constant main body pull rate during growth for at least about 90% of the length of the main body of the single crystal silicon ingot. 
     
     
       28. The method of  claim 1  wherein the main body pull rate is a constant critical pull rate sufficient to avoid agglomerated point defects over at least 70% of the length of the main body of the single crystal silicon ingot. 
     
     
       29. The method of  claim 1  wherein the main body pull rate is a constant critical pull rate sufficient to avoid agglomerated point defects over at least 90% of the length of the main body of the single crystal silicon ingot. 
     
     
       30. The method of  claim 1  wherein the volume of molten silicon varies by no more than about 1.0 volume % during growth of at least about 90% the main body of the single crystal silicon ingot. 
     
     
       31. The method of  claim 1  wherein the volume of molten silicon varies by no more than about 0.5 volume % during growth of at least about 90% the main body of the single crystal silicon ingot. 
     
     
       32. The method of  claim 1  wherein the volume of molten silicon varies by no more than about 0.1 volume % during growth of at least about 90% the main body of the single crystal silicon ingot. 
     
     
       33. The method of  claim 1  wherein the melt elevation level varies by less than about +/−0.5 millimeter during growth of at least about 90% the main body of the single crystal silicon ingot. 
     
     
       34. The method of  claim 1  wherein the main body of the single crystal silicon ingot comprises perfect silicon over at least about 70% of the length of the main body of the single crystal silicon ingot. 
     
     
       35. The method of  claim 1  wherein the main body of the single crystal silicon ingot comprises perfect silicon over at least about 80% of the length of the main body of the single crystal silicon ingot. 
     
     
       36. The method of  claim 1  wherein the main body of the single crystal silicon ingot comprises perfect silicon over at least about 90% of the length of the main body of the single crystal silicon ingot.